Sending and Receiving Data
/* Each TX or RX packet must contain a 16 byte control header that is
 * used to *p
ass protocol specific information to the driver. Note, API header does
not *get
transmitted. */


/* In this case, we loop until certain number of packets are transmitted
 * or an *
Event occurs */

        for(;;) {

/* Initialize the select() variables for receiving, transmitting, and
 * oob/event *data */
                FD_ZERO(&readset);
                FD_ZERO(&oobset);
                FD_ZERO(&writeset);

                FD_SET(sock,&readset);      
                FD_SET(sock,&oobset);
                FD_SET(sock,&writeset);


/* Select() system call can timeout due to link inactivity. This option
 * is not * being used in this example */
                tv.tv_usec = 0;
                tv.tv_sec = TIMEOUT;


/* The select function must be used to implement flow control.
 * WANPIPE socket will block if socket buffers are full.
 * Select system call can monitor arbitrary number of sockets  */

                if((err=select(sock + 1,&readset, &writeset, &oobset,
&tv))){

/* Select() received a signal from the socket,
*  we must check which operations are allowed */

if (FD_ISSET(sock,&readset)){

        /* Socket has incoming data, use recv() system call to obtain
* the incoming packet */
                              err = recv(sock, Rx_data, sizeof(Rx_data), 0);

/* Handle received data ... */


}else if (FD_ISSET(sock,&writeset)){

        /*Socket buffers are not full and data can be transmitted
* create a packet and use send() system call to pass data to the driver
* */

        err = send(sock, Tx_data,
Tx_lgth + sizeof(x25api_hdr_t),0);

/* Handle any errors or other any other logic ...*/

}else if (FD_ISSET(sock,&oobset)){

/*An error has occurred during X25 operation.  We must receive the OOB
 * packet
* then determine and handle the error condition*/

        err = recv(sock, Rx_data, sizeof(Rx_data), MSG_OOB);

/* Handle an error and any other logic ... */
}
} /*End of socket() call */
}/* End of for(;;) loop */

Once data transfer is complete, a connection is terminated using the close() 
system call */
close(sock);